Typically, electronic apparatus such as notebook or laptop computers have a first unit having a keyboard that is coupled by hinges to a second unit having a display screen, such that the two units can be opened and closed relative to each other. When the apparatus is used, the second unit is opened, and when it is not used, the second unit is closed such that the display screen lies on the keyboard. This type of apparatus is well known as a notebook personal computer (hereinafter referred to as a notebook PC).
Another type of portable computer includes a display screen, wherein the display screen is configured to recognize a stylus or pen-like device that is placed close to or in contact with the screen to enable user input. This type of apparatus is well known as a tablet personal computer (hereinafter referred to as a tablet PC).
Recently, convertible tablet/notebook computers have become available with the first unit and the second unit coupled through a two-axis coupling device which allows rotation of the second unit in two directions relative to the first unit. This configuration allows the computer to be used either as a notebook PC with the display screen projecting upward from the keyboard, or as a tablet PC with the display screen resting facing up on the keyboard (refer to Japanese Patent Application Publication No. 11-312876).
As for Notebook PCs, typically, a projection for detecting the opened/closed status of the display screen (second unit) relative to the keyboard (first unit) is provided in the rear of the keyboard disposed on the top surface of the first unit. When the second unit is closed, the projection is pushed into the second unit so that the closed status is detected. This is an open/close detection means. In this case however, it happens that the user's finger accidentally touches the projection causing the notebook PC to incorrectly recognize that it has entered the closed status.
Some notebook PCs incorporate another type of open/close detection means in which a small hole is formed in the rear of the keyboard of the first unit whereas a projection to be inserted into the hole is formed below the display screen of the second unit. When the second unit is closed, the projection is inserted into the hole so that the closed status is detected. In this case, the hole is smaller than the tip of a finger, which prevents the notebook PC from incorrectly recognizing that it has entered the closed status unlike the previously mentioned open/close detection means.
Some convertible tablet/notebook computers are well known for having a rotation detection means for detecting the direction of the second unit (display screen) in addition to the open/close detection means of the notebook PCs. This type of computer has the following deficiencies.
In order to change the convertible tablet/notebook computers from notebook PC mode to table PC mode, the user turns the display screen facing forwards by 180° so that the back of the display screen faces forwards and the user lays the back of the display screen on the keyboard.
The rotation detection means is to detect the change of the direction of the display screen to turn images displayed on the display screen by 90° because, typically, images displayed on the display screen in notebook PC mode need to be turned 90° to be displayed in table PC mode in convertible tablet/notebook type of computers. Thus, if the user turns the display screen 180° to change the computer from notebook PC mode to tablet PC mode, the rotation detection means detects the change of the direction of the display screen so that images displayed on the display screen is turned 90°. However, there occurs the following unfavorable situation. During the use in notebook PC mode with the display screen opened, the user may turn the display screen 180° to show it to the person opposite to the user. Then the images are unexpectedly turned 90° for use in table PC mode because the change of the direction of the display screen is detected by the rotation detection means. The images turned 90° are difficult to see for the person opposite to the user because the orientation of the images on the display screen is still in notebook PC mode.
Also, the open/close detection means incorporated in convertible tablet/notebook computers has the following deficiency. As mentioned before, the open/close detection means of the type having a projection arranged below the display screen has no problem when it is incorporated in the notebook PCs. However, if this type of open/close detection means is incorporated in a convertible tablet/notebook computer, the projection projects from the top surface of the closed computer when the computer is in table PC mode, i.e. the projection projects upward beside the screen display, which is not appropriate in terms of design.
There is another type of open/close detection means known in the field of mobile phone, which is composed of a magnetic sensor and a magnet and incorporated in a mobile phone having two units coupled through a two-axis coupling section (refer to Japanese Patent Application Publication No. 2003-174495). This type of detection means can be incorporated in convertible tablet/notebook computers.
The detection means disclosed in Japanese Patent Application Publication No. 2003-174495 is arranged in the following manner. One set of a magnetic sensor and a magnet is disposed close to the coupling section of the two units whereas another set of a magnetic sensor and a magnet is disposed away from the coupling section. If this structure is adopted by convertible tablet/notebook computers, a magnet sensor is arranged close to a position where the wrist of a user is rested. If the user wearing a magnetic bracelet uses the computer in this situation, the bracelet would cause false detection.